The present invention relates to a system for operating an internal combustion engine.
Various attempts have been made to improve performance of an internal combustion engine.
Japanese Patent Application Second Publication No. 2-43004 discloses a system for operating an internal combustion engine, in which opening and closing timings for an intake valve or exhaust valve and valve lift thereof are variably controlled under low-speed and high-speed operating conditions of the engine.
An object of the present invention is to improve a performance of the engine, and especially to achieve a stable engine operation within low-speed/low-load operating range and an improved fuel economy at low-speed/medium-load operating range in which the engine is often operated during driving in an urban area.